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[217.213.144.15]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5bfca5bb57asm1109637e87.74.2026.10.29.03.08.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Oct 2026 03:08:13 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 29 Oct 2026 11:08:10 +0100 To: Herbert Xu Cc: "Liam R. Howlett (Google)" , Uladzislau Rezki , Michal Hocko , Baoquan He , Alexander Potapenko , Andrey Ryabinin , Marco Elver , Michal Hocko , Linux Crypto Mailing List , Andrew Morton , Thomas Graf , linux-mm@kvack.org, linux-kernel@vger.kernel.org, maple-tree@lists.infradead.org, Lorenzo Stoakes , Chris Mason , Alice Ryhl , Andrew Ballance , stable@vger.kernel.org, "David Hildenbrand (Arm)" Subject: Re: [PATCH 4/4] rhashtable: fix vmalloc() deadlock in atomic rehash Message-ID: References: <20261028154218.1668182-1-liam@infradead.org> <20261028154218.1668182-5-liam@infradead.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Oct 29, 2026 at 10:16:36AM +0800, Herbert Xu wrote: > On Wed, Oct 28, 2026 at 11:42:18AM -0400, Liam R. Howlett (Google) wrote: > > > > Below, one CPU adds an FDB entry for an RTM_NEWNEIGH netlink request, > > while another CPU is inside vmalloc() or vfree(): > > > > RTM_NEWNEIGH vmalloc() or vfree() > > ============ ==================== > > spin_lock_bh(&br->hash_lock) > > spin_lock(&vn->busy.lock) > > rhashtable_insert_rehash() > > kvmalloc(GFP_ATOMIC) > > vmalloc() > > spin_lock(&vn->busy.lock) > > waits for the other CPU > > softirq: a frame for the bridge > > spin_lock(&br->hash_lock) > > waits for RTM_NEWNEIGH > > I think this is a fundamental bug in the kvmalloc non-blocking > support patch. How can it be used at all if it is susceptible > to such dead-locks? > > And if you can't use it safely why don't we just get rid of the > broken kvmalloc non-block path and have it always go to kmalloc > like it did before? > If we have a look at this as we did not have vmalloc() here: RTM_NEWNEIGH foo() or ... ============ ==================== lock_bh(&br->hash_lock) foo() lock(B) rhashtable_insert_rehash() foo() lock(B) waits for the other CPU softirq: a frame for the bridge lock(&br->hash_lock) waits for RTM_NEWNEIGH Same issue? I have a question: GFP_ATOMIC/GFP_NOWAIT guarantee they do not sleep. Do they guarantee not hitting ABBA dead-locks or they are not interrupted? -- Uladzislau Rezki